A sintered compact is obtained by subjecting mixed metal powder to compression molding, and then sintering the resultant at a predetermined temperature. The sintered compact is employed for a machine part and the like, because the sintered compact enables production of a net shape product or a near-net shape product and hence a reduction in cost can be achieved through an increase in yield and a reduction in number of processing steps. Of such sintered compacts, an iron-based sintered compact is widely employed for an automobile part, an electric product, and the like by virtue of excellent mechanical properties.
However, many pores remain in the inside of the sintered compact. Those pores serve as stress concentration sources to show behavior such as cracks in an ingot material, which causes a reduction in static strength, such as tensile/compression/bending strength or impact strength, and a reduction in dynamic strength, such as fatigue strength.
For example, there is known a technology for realizing densification of the sintered compact by alternately performing a compression molding step and a sintering step twice on the mixed powder (for example, Patent Literature 1). However, in this case, there is a problem of a rise in production cost.
For example, in Patent Literature 2, densification of the sintered compact is realized by using metal powder having a coarse particle size distribution without using costly treatment, such as the two-stage molding and two-stage sintering.